345. 反转字符串中的元音字母

class Solution {
    public String reverseVowels(String s) {
        if (s == null) return null;
        HashSet<Character> arr = new HashSet<>(Arrays.asList(‘a‘, ‘e‘, ‘i‘, ‘o‘, ‘u‘, ‘A‘, ‘E‘, ‘I‘, ‘O‘, ‘U‘));
        //定义一个左指针
        int left = 0;
        //定义一个右指针
        int right = s.length() - 1;
        char [] res = new char[right + 1];
        while(left <= right){
            char cleft = s.charAt(left);
            char cright = s.charAt(right);
            if (!arr.contains(cleft)){
                res[left++] = cleft;
            }
            if (!arr.contains(cright)){
                res[right--] = cright;
            }
            if (arr.contains(cleft) && arr.contains(cright)){
                res[left++] = cright;
                res[right--] = cleft;
            }
        }
        return new String(res);
    }
}